This invention relates generally to fuser apparatus and more particularly to fuser apparatus including means for positively separating a support after fusing.
In the electrographic process, a toner image corresponding to an original is formed on a support such as a copy sheet. The toner is of heat and/or pressure fusible particles and the toner image is permanently fixed to the support by means of fuser apparatus which includes a fuser member, such as a fuser roller, which contacts a support carrying a toner image to fuse the toner image by means of heat and pressure. Since there is a tendency for a support to stick to the fuser member, a separating member is frequently employed to positively separate the support from the fuser member. The separating member has an end which may contact the surface of the fusing member or which may be disposed slightly above the surface. Such arrangements increase the danger, however, that the support will slip between the fusing member and the separating member and cause jamming of the paper and possible breakage of the end of the separating member.
In order to minimize this problem, it has been proposed to provide the surface of the fuser member with undulations or slots into which the end of the separating member penetrates. Thus, in U.S. Pat. No. 2,701,765, issued Feb. 8, 1955, for "Xerographic Fusing Apparatus," a heated drum is provided having open grooves into which stripper feelers penetrate in order to strip a fused sheet from the drum. U.S. Pat. No. 3,845,742 issued Nov. 5, 1974, for Fuser Roll Construction, discloses a fusing system including a rotatable member covered with an elastomeric material formed with undulations to accommodate stripper fingers. The undulations have a depth and width sufficient to cause a fused sheet to assume the shape of the undulations to improve sheet separation. In the apparatus of the latter two patents the slots or undulations are open so that there is a tendency for toner and other debris to accumulate in the slots. Moreover, the width of the undulations and slots may cause image defects in a fused image. Such problems are minimized somewhat in British Patent Specification No. 1,456,239, published Nov. 24, 1976, for "Fixing Device," which discloses a fuser roller having an elastomeric coating with a plurality of narrow grooves into which stripper wires or blade-like members penetrate to strip copy sheets from the roller after fusing. Although the grooves are open at the top, in an embodiment described at Page 5, Line 41 and following, the depth and width of the grooves are such that in the roller nip the sides are nipped together so that the surface of the roller shows an even surface in the nip. However, since the slots are open substantially about the entire periphery of the roller, there is still a tendency for toner and other debris to accumulate in the slots, thus increasing the likelihood that copy sheets passed through the fuser roller nip will pick up debris which is scavenged out of the slots by the stripper members. In this regard, it should be noted that in the embodiment shown in FIG. 1 of the British specification, cleaning rollers are provided; however, these rollers only bear against the surface of the fuser roller and do not clean the slots thereof.
In the above three patents, no release material such as fuser oil is applied to the fuser roller. If such material were applied, it would also tend to accumulate in the open slots thus increasing the probability of image defects in a fused support.